Conventionally, as an installing and using method of a welding multi-joint robot (an industrial robot), floor-mounted use, ceiling-mounted use, or the like, is generally known. FIG. 6 is a perspective view showing such an industrial robot when it is used in a state in which it is mounted on a floor. FIG. 7 is a side view showing such an industrial robot when it is used in a state in which it is mounted on a ceiling.
First arm 112 rotates with respect to base 111 for installation. Second arm 113 pivots with respect to first arm 112, and third arm 114 pivots with respect to second arm 113. Furthermore, fourth arm 115 pivots with respect to third arm 114. Welding wire feeder 116 feeds a welding wire. Fixing device 117 fixes welding wire feeder 116 to the industrial robot. Torch cable 118 feeds the welding wire from welding wire feeder 116 to welding torch 119.
In FIG. 6, welding wire feeder 116 is fixed to the upper part of third arm 114. Such a configuration is disclosed in, for example, Japanese Patent Unexamined Publication No. 2004-261878. Furthermore, in FIG. 7, welding wire feeder 116 is fixed to the side face of third arm 114. Such a configuration is disclosed in, for example, Japanese Patent Unexamined Publication No. H8-57648. Thus, in a conventional welding multi-joint robot, the position to which welding wire feeder 116 is attached is different between the time of floor-mounted use and the time of ceiling-mounted use. That is to say, the structure (specification) is generally different between the floor-mounted use and the ceiling-mounted use.
Therefore, when a robot used in a state in which it is mounted on the floor is used in a state in which it is mounted on the ceiling, or when a robot used in a state in which it is mounted on a ceiling is used in a state in which it is mounted on a floor, the position to which welding wire feeder 116 is attached has to be changed. In order to correspond to such a change, it is necessary to provide fixing positions of wire feeder 116 for both floor-mounted use and ceiling-mounted use. That is to say, two or more positions to which wire feeder 116 is attached need to be provided. Furthermore, it is necessary to prepare attaching members for fixing welding wire feeder 116 corresponding to each use form of floor-mounted use and ceiling-mounted use. Thus, it takes a time to change the use forms, and the cost therefor rises.
Furthermore, in coupling of a feeder cable for electrically coupling between welding wire feeder 116 and the inside the robot, it is necessary to additionally consider a wiring method corresponding to each use form. Thus, it takes a time to change the coupling corresponding to the use form.
Furthermore, in the structure shown in FIG. 7, welding wire feeder 116 is attached to the side face of third arm 114. Therefore, the distance between a location of the center of gravity of welding wire feeder 116 and the industrial robot (the arm) is increased, and a moment load to fixing device 117 for attaching welding wire feeder 116 is increased.
In order to resist this load, the strength and rigidity of fixing device 117 is required to be increased. That is to say, the size and mass of a member constituting fixing device 117 may be increased. Such a configuration deteriorates the motion performance of the industrial robot and adversely affects the approaching performance to a welding work and a jig for fixing the welding work.